It has to do with the amount of 'G' the autopilot is allowed to apply. We had quite a bit of trouble with this a few years back, particularly when stowing the speedbrake on descent. Boeing introduced a mod that increased the amount of 'G' authority to the A/P, which improved the problem. It is still sluggish, but better than it used to be.
In cruise is a different matter. That is simply related to the autothrust.